My invention relates to an override arrangement and actuating handle for a shifting mechanism in portable tools which prevents the operator of such a tool from inadvertantly overriding a stop position of the shifting mechanism.
Power driven portable tools usually include a transmission for connecting the drive motor of the tool to the output of the tool where a tool element is attached for performing the work on the workpiece. The transmission usually is contained in a gear case attached to a housing for the drive motor and includes a set of gears for reducing the speed of the bit to a useable level as well as for increasing the torque output available at the output of the tool.
In the case of a two-speed power tool, there is usually provided a mechanical transmission which utilizes one or more sliding gears, or else a sliding gear cluster, to shift from one speed to another. The gears are alternately engaged and disengaged from the drive mechanism with the aid of a shifting mechanism. The shifting mechanism usually has a shaft which can be rotated to achieve the desired gear engagement for a specific operating speed. One end of the shaft penetrates the gear case wall and has a handle attached thereto which is manually actuable by the operator of the tool. Typically, the handle is rotated between two positions corresponding to respective speeds at which the tool is to operate. If excessive force is utilized to rotate the handle, the shaft can be rotated beyond one of its end position possibly causing damage to the transmission.
In some tools such as a power-driven portable combination drill and screwdriver, the transmission will include a clutch so that the tool may be adjusted to provide either a positive drive connection between the motor and the tool element or a drive connection that can be established and interrupted at will by the person operating the tool when required by the nature of the work. Such a combination tool can include a shifting mechanism that has a rotatable shaft penetrating the gear case as suggested for example, in a patent application entitled: "Power-Driven Drill and Screwdriver" of Robert Gordon Moores, Jr., and Charles Edward Hopkins, Sr., filed on June 15, 1977, and having Ser. No. 806,907.
In the case of the power driven drill and screwdriver, there is a clutch arrangement which is actuable to disconnect the tool element from the drive motor. The clutch arrangement includes two clutches having respective sets of clutch teeth formed thereon. The shifting mechanism is actuated to engage and disengage the clutch teeth corresponding to the screwdriving and drill modes of the tool. If the teeth are too tightly engaged when the operator places the tool in the drill mode, damage can occur for example at the interface of the one of the clutch members and the portion of the shifting mechanism engaging the same. Accordingly, it is desirable that some means be provided to prevent the operator of the tool from inadvertantly rotating the shaft of the shifting mechanism beyond the limit position corresponding to the drill mode.